The present invention relates to an internal combustion engine peripheral cam having a cam contour, and more particularly, to a cam contour which generates at least one positive acceleration course in the valve opening area, with an opening acceleration course which had two acceleration curves with relatively high acceleration peak values of different amounts spaced by means of an intermediate curve of a relatively low positive acceleration.
For achieving high specific operations for a close torque, on one hand and a high power on the other hand, internal-combustion engines are conventionally provided with a valve timing which has very xe2x80x9csharply definedxe2x80x9d valve lift courses for the inlet and outlet valves in order to obtain the desired flow rates by way of correspondingly rapidly changing valve opening cross-sections. With rapidly opening outlet valves, a very high exhaust lead push is therefore generated which causes a non-uniform outflow of the exhaust gases. Since, however, the exhaust gas acoustics are very significantly influenced by the form and the amplitude of the exhaust lead push, a lead-out noise occurs in a high flow rate and a high opening acceleration of the outlet valve which has a high proportion of higher harmonics. This results in an intensified disadvantageous surface radiation of the exhaust gas system and of the internal-combustion engine.
In known production engines with large outlet cross-sections generated by several outlet valves per cylinder unit and high opening accelerations produced by sharply defined valve lift courses, this problem was solved in that the outlet cams provided for controlling the outlet valves per cylinder are arranged in an angularly offset manner with respect to one another (phasing). This arrangement which is, for example, also described in DE-C 39 33 021 or Japanese Patent Application 1-159 417 has the considerable disadvantage that each cam has to be ground separately.
The high-expenditures phasing arrangement described in DE-C 195 21 141 or U.S. Pat. No. 5,647,310, in the case of an outlet cam, is replaced in that its cam contour causes an asymmetrical valve acceleration curve with an opening acceleration curve whose maximal value is lower than that of the closing acceleration curve. However, such an asymmetrical outlet valve acceleration curve is known from the book xe2x80x9cA Decade of Continuous Challengesxe2x80x9d published by Honda Co. in Japan in 1993 under No. ISBN 4-9900262-0-9, from the illustrations on pages 136 and 137.
It is known that the surfaces under the closing acceleration curve and the opening acceleration curve should be the same so that the base of the known opening acceleration curve having approximately 50% of the maximal value of the closing acceleration curve extends along a larger angle-of-rotation range of the cam on the abscissa. Such a widening of the base of the acceleration curve also exists by way of the above-described phasing arrangement during the opening of several outlet valves of a cylinder by the superpositioning of the individual opening acceleration curves. Consequently, a predetermined widening of the base, while taking into account the above-mentioned sameness of the surfaces, causes each opening acceleration curve to be reduced in its maximal value for reducing an exhaust lead push.
Further, an opening acceleration course for a peripheral cam with two relatively narrowly adjacent acceleration curves of different maximal values along a joint broad base is known, for example, from FIG. 38, page 85 of xe2x80x9cEtude Dynamique de la Distribution dans les Moteurs à Combustion Internexe2x80x9d.
An object of the present invention is to dimension the cam contour of the peripheral cam at least for the valve opening area such that the gas dynamics of the internal-combustion engine on the outlet side and/or the inlet side are favorably influenced by way of the opening acceleration course.
This object has been achieved by providing that the first acceleration curve has a peak value of approximately 40 to 60% of a peak value of the adjacent second acceleration curve set at 100%, and in that the ascending curve section of the first acceleration curve and the descending curve section of the second acceleration curve form at least one projected intersection respectively with the zero acceleration line on the abscissa, the distance between respective connection points of the descending curve section of the first acceleration curve and of the ascending curve section of the second acceleration curve with the intermediate curve corresponding to an amount of 10 to 15% of the distance of the abscissa intersections set at 100%.
An advantage of the present invention is an opening acceleration course with two acceleration curves for whose connecting intermediate curve, a dimensioning range is indicated which is advantageous with respect to the extent of the acceleration delay. Thereby, when the peripheral cam dimensioned according to the present invention is used as an outlet cam for actuating an outlet valve, an exhaust lead push which is critical with respect to the exhaust gas acoustics is securely avoided. For an internal-combustion engine with several outlet valves per cylinder, another advantage is that an angularly offset arrangement of the outlet cams for a cylinder unit is unnecessary and therefore all outlet cams can be machined by one grinding wheel.
The opening acceleration course according to the present invention with a first acceleration curve and a second acceleration curve which is higher than the first has, in a further embodiment of the present invention for an intermediate curve connecting the two acceleration curves, a dimensioning range which is advantageous with respect to the extent of the acceleration delay.
In a further feature of the present invention, measurement ranges of the two acceleration curves of the opening acceleration course which have different levels relate to the abscissa of an acceleration diagram. The measurement range or lay-out range which is relatively larger particularly for the first acceleration curve, in conjunction with a constant acceleration in the summit range of the first acceleration curve and a constant acceleration of the intermediate curve between their connection points by way of these steadying sections results in an acceleration delay which has an advantageously favorable effect on the gas dynamics.
This acceleration delay achieved according to the present invention causes on the outlet side a significant reduction of the lead-out noise and thus of the surface radiation. On the inlet side, the opening acceleration course according to the present invention has a delay for a dynamic gap formation to increase the gas velocity for whirl formation.